1) Field of the Invention
The present invention relates to a multi-area white-balance control device, a multi-area white-balance control method, a multi-area white-balance control program, a computer in which a multi-area white-balance control program is recorded, a multi-area white-balance image-processing device, a multi-area white-balance image-processing method, a multi-area white-balance image-processing program, a computer in which a multi-area white-balance image-processing program is recorded, and an image-capture apparatus provided with a multi-area white-balance image-processing device for achieving color reproduction without unnaturalness over the entirety of an image that is captured of a scene lighted by a plurality of light sources, by estimating color temperature for each of areas into which the image is divided and performing white-balance correction.
2) Description of Related Art
A photographic lighting source changes its color temperature depending on solar altitude, atmosphere conditions etc., for example in the daytime outdoors. In addition, the color temperature differs depending on whether the place is sunny or shady.
Regarding indoor photography, there are various types of artificial lighting such as by a fluorescent lamp, an incandescent lamp, etc. which are different in color temperature.
When flash is used in photographing outdoors in the daytime, mixture of the flash light and the natural light forms a photographic lighting source.
When flash is used in photographing outdoors in the nighttime, the flash light and the background artificial light are not mixed, but the color temperature of lighting in the very scene varies with areas in the scene.
When flash is used in photographing indoors, the flash light and the artificial light are mixed to forma photographic lighting source.
Under the various conditions of photographic lighting source as stated above, human eyesight causes color adaptation. That is, according to the human eyesight, a white object in the area of attention is sensed white irrespective of whether the light source is sunlight, artificial light, or mixed light of these. In conformance with this characteristic of the human eyesight, a camera as an input device is configured to control RGB gains, to perform so called “white balance” processing.
However, since a camera cannot know the photographic lighting source before shooting, upon the type of photographic lighting (color temperature of the photographic lighting source) being assumed on the basis of an image captured by photographing or being designated by a user, correction of the white balance over the entire image is made in conformance with this type of lighting, in general.
In a case where the scene about an object is lighted by a plurality of light sources, in order to highly accurately perform white-balancing over the entire image irrespective of color temperature of the photographic lighting source in the areas in the scene, it is necessary, upon dividing the acquired image into a plurality of division areas, to detect color temperature of the photographic lighting source for individual division areas and perform different white-balance processing.
Regarding a conventional method of white-balance processing for an image captured by photographing a scene lighted by a plurality of light sources, Japanese Patent KOKAI No. 2010-213232 for example discloses: dividing a frame for image capture into a plurality of regions in accordance with lightness information and color information; setting white-balance correction coefficients differing with the plurality of regions; and generating white-balance correction coefficients for the entire frame for image capture upon setting a white-balance correction coefficient limit for limiting, within a predetermined range, differences among the plurality of white-balance correction coefficients for individual plurality of regions; for the purpose of solving the problem that a plurality of illumination areas derived from different kinds of light sources in one frame for image capture make it difficult to achieve appropriate white balance over the entire frame for image capture and thus generate a color shift in a captured image.